A typical Saturday. I am a passenger in husband's car, the car I refuse to contribute to financially on the grounds that there was nothing wrong with the old one and that cars are ecologically unsound even though this one has a catalytic converter. So we are straight into the Conjugal Conflict Zone.

Conflict One revolves around ventilation. In the winter, I like to have the heater on and the windows open (for fresh air). Husband, suddenly stricken by global-warming conscience, believes it should be one or the other. In the summer, he likes to turn the fan up high (to keep the air moving); to me, this feels like a giant hair dryer farting fumes in from the wreck in front, so I prefer the vents closed.

Round One is mildly physical: heating dial flicked up, heating dial flicked down, vents opened, vents closed. This is followed by a pointless rehearsal of our air-conditioning preferences. And that's it really: a reflex action which doesn't escalate into a fight because I end up keeping my window a tiny bit open, or close the vents on my side.

All this is a warm-up, however, for Conflict Two, the big one, the one which makes me think we ought to be in Emergency Marital Therapy. It happens as soon as husband hits a clear stretch of road and increases his speed to 40 mph. I ask him to slow down; he says no. I ask him why he can't stick to the speed limit; he says nobody else does. I tell him he's more likely to be involved in an accident; he says he's a good driver. I remind him that I am the member of the household who has never had an accident; not his fault, he counters. I appeal to him as a cyclist: doesn't he hate it when cars burn up behind him on the Camberwell Road? There are no cyclists on this road, he says. Then I ask, super-rationally, if we can do a deal: he agrees to stick to 30 mph and I will never criticise any aspect of his behaviour ever again; he doesn't believe me. So then I start screaming: does he want to kill us both or does he simply enjoy scaring me? Husband - frustratingly hard to provoke - says I always exceed the speed limit, and carries on driving at 40 mph.

I may die quite soon under the wheels of the lorry in front or perhaps from a rage-related heart problem. But I want to die knowing whether back- seat driving is more likely to cause or prevent death on the road. Is it part of my civic duty, or a metaphorical stage on which my husband and I are battling for power? To put it bluntly: am I in the right?

"A lot of men used to write to me about pain-in-the-rear back-seat drivers who drove them bonkers," wise old Marge Proops once an explained to a hen-pecked wife. "Mothers-in-law, usually, but there were plenty of wives who couldn't keep their mouths shut. Now that large numbers of women drive, they're getting a taste of what men had to put up with for years." Meanwhile, a Nottingham driver who killed two passengers (his pregnant wife and a neighbour) blamed his pet dog, an over-excited stepchild and - gulp - his wife's back-seat driving.

By now in a state of mild anxiety I call the AA, from whom I learn that 95 per cent of men feel totally or fairly relaxed when they are driving with their partner. The typical male "enjoys motoring and sees himself as a very good and very confident driver". Husband, on the other hand, is a member of an oppressed, unrelaxed minority, like the Kurds, or men with red hair. Worse, he is oppressed for being normal: according to a study of Manchester drivers by road psychology expert Jim Baxter, 75 per cent of them ignore the 30 mph speed limit.

Almost as bad, I am a danger on the road. "Constant nagging can distract, increase stress levels and therefore the chance of an accident,'' confirms the man in the AA press office. "Plus, being on the brink of an argument can make you drive aggressively. As a rule," he recommends, "button it."

Button it? On the cusp of going into self-help (Smart Women, Foolish Driving Habits?), I recall a television series on driving produced by the ultra-respectable Department of Transport and the BBC. Programme one tackled speed. And yes! More than 300 lives would be saved every year if motorists cut their average speed by just one mile an hour. In programme six, devoted to passengers, presenter Alexei Sayle encouraged us to be more assertive when accompanying speeding motorists. Better still, husband is now beginning to look like the oppressive minority, since normal people drive better with friends, relatives, partners or children in the car.

Then I come across the fact sheet. Every year nearly 1,000 people are killed on the road by drivers who are going too fast for the conditions. When pedestrians are hit by a car, at 20 mph one child in 20 is killed; at 30 mph half are killed; at 40 mph most are killed. Most casualties occur in built-up areas.

My confidence soars. "There's no doubt", says the AA road safety officer, "that women - including my wife - complain more about men's driving. But", he adds, "objective studies have shown that people being accused of driving too fast are driving too fast. Men are simply less sensitive to feelings and advice. Really, it's sexism. Criticising a man's driving is like criticising his performance in bed. But make your point, even if tact and diplomacy fail. And keep on making it."

And so the back-seat driving issue is resolved. Next time we're racing down Camberwell Road I'll simply tell my husband that he's sexist, insensitive and neurotic about his performance in bed. Voila!